This invention pertains to patterned surface friction materials for use in clutch plate members, brake pads, transmissions and the like, and methods of making and using these constructions.
Friction materials are used in a wide variety of different automotive applications such as for brake linings, brake pads, for torque converter clutches in automatic transmissions, synchronizer rings in manual transmissions, and in so-called xe2x80x9cslippingxe2x80x9d clutches in newer automobiles (a variation of a torque converter clutch).
In general, friction materials need to meet requirements in a wide variety of properties. Desired attributes of a friction material include toughness, strength, heat resistance, good frictional properties, and long life. Friction materials for transmissions should have a generally level torque curve, display no bond failure under standard usage conditions, and have retention of torque curve levelness and torque capacity. In addition, as smooth operation of the clutch is enhanced by friction modifiers in the transmission fluid, the friction material should hold or retain an appropriate amount of fluid at the engaging surface. Towards these and other objectives, patterned or textured friction surfaces for a friction material have been proposed heretofore.
One method to make such a patterned surface for a friction material is by a batch thermocompression molding process, such as disclosed in U.S. Pat. No. 5,004,089 (Hara et al.), wherein the mold has essentially the inverse shape of the desired dimpled surface. Since the molding processes are generally batch processes that require considerable time and energy, they are disfavored for large scale production facilities. U.S. Pat. No. 3,841,949 (Black) describes a composite friction plate provided with a facing of synthetic rubber presenting small islands in which friction material, such as sintered powdered bronze particles, is embedded to form the actual friction surface. Preferably, such particles or lands are said to be in the shape of circular buttons, which project from a thin base of an outer coating, such as heat resistant synthetic rubber, and are distributed over the base in spaced relation to each other. This arrangement is said to reduce the requirements for the quantity of cooling oil needed for the dissipation of a given amount of heat in the clutch or brake.
Abrasive articles are known having a contoured topography abrasive layer characterized as being a three-dimensionally shaped, radiation-cured dispersion of abrasive particles in an organic binder, such as described in U.S. Pat. No. 5,152,917 (Pieper et al.). This patent in general describes abrasive materials made by coating a slurry of UV curable resin and abrasive particles onto a patterned surface, contacting the slurry-coated patterned surface with a backing, curing the resin, and removing the finished abrasive article from the patterned surface. However, the abrasive materials as described therein are inadequate for use as friction materials, they do not have the combination of ingredients commonly used in friction materials needed to meet the rigorous standard tests for friction materials used in automotive transmissions. Also, as described in U.S. Pat. No. 5,234,740 (Reeves et al.), slip control sheeting is known comprising a backing having first and second major surfaces with an array of protrusions on the first major surface, useful for covering, e.g., gymnastics apparatuses, and tool and racquet handles. The protrusions formed in Reeves et al. do not contain granular carbon friction particles, among other things, needed to provide a friction material suitable for automotive transmission applications, such as a clutch plate member.
U.S. Pat. No. 5,083,650 (Seitz et al.) disclose a friction member having a roughened surface suitable for use as a friction facing member in a transmission. The friction member of Seitz et al. involves a heat-resistant paper supporting granular carbon friction particles resin-bonded via underlying and overlying thermoset polymeric binder containing carbon filler particles. An undulated (roughened) contour is formed on the surface of the friction member of Seitz et al. It would be desirable to form a friction facing layer with increased texture control and without the need for providing sequential coatings as employed in Seitz et al.
In accordance with the present invention, friction materials and clutch plate members are presented having a patterned friction surface. Methods of making and using the inventive friction materials are also presented. One embodiment of the invention is a friction material for a friction facing member, the friction material comprising: a backing having a front surface and a rear surface, and a plurality of precisely shaped composites forming a patterned friction coating on the front surface of the backing, the precisely shaped composites comprising a plurality of friction particles dispersed in a binder.
The plurality of precisely shaped friction composites define an overall friction surface topography having a three-dimensional pattern, such as an array having a non-random pattern. This patterned friction surface generally comprises a plurality of peaks or asperities associated with the shape of each friction composite, with adjacent friction composite peaks or asperities separated from one another. Since the peaks are separated from one another, cavities are formed therebetween. These cavities provide a means for dynamically retaining a fluid, e.g., transmission fluid. The precisely shaped friction composites each have a precise shape defined by a distinct and discernible boundary. Adjacent shaped composites are preferably the same shapes, although different shapes are also contemplated to be within the scope of the invention. It is preferred that the composites are equally spaced apart, although random spacing is also contemplated within the scope of the invention.
Preferably, each of the plurality of precisely shaped friction composites comprise a three-dimensional shape selected from the group of parallelpiped, cubic, conical, truncated pyramid, cylindrical, pyramid, and mixtures thereof, more preferably, each of the plurality of precisely shaped composites comprise a pyramid having a triangular-shaped base, even more preferably, each of the plurality of precisely shaped friction composites comprise a pyramid having a quadrilateral-shaped base, and most preferably, each of the pyramids include flat upper surfaces. Optionally, the precisely shaped composites may further comprise an additive.
In another embodiment, the friction material is resilient, i.e., the friction material has an elastic modulus of about 107 dynes/cm2 or less, and more preferably about 106 dynes/cm2 to about 107 dynes/cm2. Elastic modulus typically is determined using a Rheometrics Solids Analyzer Model RSA II, from Rheometrics Scientific, of Piscataway, N.J. In one preferred embodiment, the friction material further comprises a tie layer on the rear surface of the backing, more preferably, the tie layer comprises a fluoroelastomer, preferably the elastic modulus is about 3.5xc3x97106 dynes/cm2. In another preferred embodiment, the elastic modulus is about 4.5xc3x97106 dynes/cm2, wherein the patterned friction coating has a coefficient of friction of about 0.14 or greater at an energy level of about 26.62 kJ.
Preferably, the friction material includes friction particles selected from the group of an organic material, a metallic material, a semimetallic material, an inorganic material, and mixtures thereof, more preferably, the friction particles comprise an organic material, even more preferably, the organic material comprises coke, wherein the coke is selected from the group of metallurgical coke, petroleum coke, coconut shell activated carbon, and mixtures thereof.
The patterned friction coating is formed from a coatable binder precursor slurry comprising a plurality of friction particles and a resin, preferably a thermosetting resin. While in the slurry form, the resin therein is not polymerized or cured. This results in the slurry being able to flow or to be coated onto the backing or into the cavities of the production tool (thus defining the term xe2x80x9ccoatablexe2x80x9d). The binder precursor slurry is then exposed to conditions such as an energy source to cure or polymerize the resin in the binder precursor slurry into a binder, resulting in the binder precursor slurry being converted into a friction coating.
As stated, although thermosetting resins are typically preferred, it is within the scope of this invention to use thermoplastic resins as binders. During the processes of this invention, the thermoplastic resin is in a molten or flowable state. Upon cooling of the thermoplastic resin, it is converted into a solidified binder and a friction composite is formed. Preferred thermoset binders are derived from addition polymerizable resins, more preferably free radical curable resins. The preferred energy source is radiation energy, such as electron beam. A particularly preferred binder comprises the polymerized reaction product of an acrylate monomer and an isocyanurate derivative having at least one pendant acrylate group. Another preferred binder is a crosslinked system prepared from an aminoplast resin having acrylamide groups, preferably from a mixture of an aminoplast resin having acrylamide groups and an aminoplast resin having acrylate groups. Another preferred binder is a crosslinked system prepared from a mixture comprising an aminoplast resin having acrylamide groups, and an aminoplast resin having acrylate groups and at least one resin having at least one pendant acrylate group. Preferably, the at least one resin having at least one pendant acrylate group is selected from the group of a monofunctional acrylate monomer, a multifunctional acrylate monomer, a urethane acrylate, an epoxy acrylate, an isobornyl acrylate, a polyester acrylate, an acrylated acrylic, a silicone acrylate, a polyether acrylate and mixtures thereof, more preferably, the at least one resin having at least one pendant acrylate group is selected from the group of a urethane acrylate, an isobornyl acrylate, a silicone acrylate and mixtures thereof. The friction material preferably has an elastic modulus of about 107 dynes/cm2 or less.
The friction material of the invention includes the backing which preferably is a nonwoven paper having a plurality of aramid staple fibers bound together by an acrylic latex.
In yet a further embodiment of the invention, a friction material for a friction facing member useful for transmitting power in a power transmission mechanism includes a nonwoven paper comprising a plurality of aramid staple fibers bound together by an acrylic latex, the paper having a from and back surface, and a pyramidal patterned friction coating attached to the front surface of the backing, the patterned friction coating comprising a plurality of precisely shaped pyramidal friction composites, each friction composite comprising a plurality of coke particles dispersed in the binder, the binder comprising a polymerized reaction product of trimethylol propane triacrylate and triacrylate of tris(hydroxy ethyl)isocyanurate.
In another embodiment of the invention, a friction material for a friction facing member includes a backing having a front surface and a rear surface; and a plurality of precisely shaped composites forming a patterned friction coating on the front surface of the backing, the precisely shaped composites comprising a plurality of friction particles dispersed in a binder, wherein the friction material has an elastic modulus of about 107 dynes/cm2 or less. Preferably, the friction material has a coefficient of friction of about 0.14 or greater at an energy level of about 26.62 kJ at about 200 cycles. More preferably, the binder comprises a crosslinked system prepared from a mixture comprising an aminoplast resin having acrylamide groups, and an aminoplast resin having acrylate groups and at least one resin have at least one pendant acrylate group selected from the group of a monofunctional acrylate monomer, a multifunctional acrylate monomer, a urethane acrylate, an epoxy acrylate, an isobornyl acrylate, a polyester acrylate, an acrylated acrylic, a silicone acrylate, a polyether acrylate and mixtures thereof, and more preferably, a urethane acrylate, an isobornyl acrylate, a silicone acrylate and mixtures thereof.
The inventive friction materials may be adhered to substrates such as metal clutch plates, synchronizer rings, brake pads, train tracks, and the like. Thus, another aspect of the invention is an article comprising one of the inventive friction materials adhered to a substrate, preferably a metal substrate. For example, in one embodiment of this invention, there is a clutch plate member for operating in a fluid medium to transmit torque to a metal mating surface situated on an opposing clutch plate member, comprising a friction facing layer constructed the same as the above-mentioned friction material that is adhesively bonded to a metal support plate. Typically, a heat resistant adhesive such as a nitrile phenolic resin is used to adhere the friction material to metal plates, although this is not a requirement.
In another embodiment of the invention, an apparatus for transmitting torque includes a first plate member for operating in a fluid medium to transmit torque to a mating surface situated on an opposing second plate member, the first plate member having a friction facing material bonded to a support plate, wherein the friction facing material comprises: a backing having a front surface and a rear surface, and a plurality of precisely shaped friction composites defining patterned friction coating attached to the front surface of the backing, the precisely shaped friction composites comprising a plurality of friction particles dispersed in a binder, and a rotating member capable of engagement with the first plate member at a friction facing material interface. This apparatus is useful in a number of torque transmitting application: wherein the first plate member and the opposing second plate member comprise a clutch; wherein first plate member and the opposing second plate member comprise a brake mechanism; or wherein the first plate member and the opposing second plate member comprise a torque converter for an automatic transmission.
In yet another embodiment, a method for altering a vehicle""s speed comprising the apparatus for transmitting torque, as described above, includes the step of engaging the first plate member in the presence of a fluid to the rotating member at a friction facing material interface such that a coefficient of friction is increased between the plate member and the rotating member to transfer the torque between the plate member ad the rotating member to alter the vehicle""s speed.
The friction materials of the invention may be employed in a variety of methods. One method of using the friction materials of the invention comprises attaching the friction material to a first member, rotating the first member in a fluid and in the presence of a second member, thereby causing the second member to be rotated. Another method of using the friction materials of the invention is to slow or stop a vehicle, the method comprising applying the friction material to a stationary member of the vehicle, rotating a second member of the vehicle in a touching fashion against the friction material, thereby increasing the coefficient of friction between the stationary member and the second member and helping to slow the vehicle. Another method of using the friction materials of the invention is to help slow a vehicle which traverses tracks, the method comprising applying the friction material to a portion of the vehicle and/or track, rotating a member of the vehicle in a touching fashion against a friction material applied to the tracks, thereby increasing the coefficient of friction between the track and the rotating member and helping to slow the vehicle.